if he didn't fuck his dad then he wouldn't be born because his father fell in love with his mother because of the sons eyes
but even before the time slip he was still born so there was another reason his dad & his mom met n they got together to have him
It’s hard to say like who came first the chicken or the egg. It’s a weird time paradox. And it not only happened to konomi and ryoi but also to konomi’s grandmother seeing a younger version of her husband. That’s why the dad is scared of the house and wants to sell it. It’s a mystery and causes some time slip. It might truly be that konomi only married her because she resembles Kyou.
If he just didn't fvck his dad then none of these would happen like dude how can you fall in love with your 14y/o dad?!